Substitute for Disqualified Player

[TGR]

I need help with this.
NCAA Rules Situation:
A1 commits his/her 5th personal foul and the official notifies the coach and player. The 20-second time limit is started with the horn to be sounded at both 5 seconds and the end of the 20 seconds. There were no substitutes at the table prior to the foul being called and Team B will have a throw-in at the spot of the foul.

Here's my question:
Does the coach have to sub for the disqualified player first, or can the coach send several subs in prior to the first horn and then finally sub for the disqualified player at the conclusion of the 20-seconds? Thanks for any help and NCAA references.